Comprehension of natural language by machines, at a near-human level, is a major goal for Artificial Intelligence. Indeed, most human knowledge is collected in the natural language of text. Machine comprehension of unstructured, real-world text has therefore garnered significant attention from scientists, engineers, and scholars. This is due, at least in part, to the fact many natural language processing tasks, such as information extraction, relation extraction, text summarization, or machine translation, depend implicitly or explicitly on a machine's ability to understand and reason with natural language.